This invention relates to new and useful improvements in electronic control indicators for cable hoist equipment and can be used for the hoist equipment of cranes or general hoists and for hoists used in the raising and lowering of drill string and the rotating of drill bits down hole.
Such equipment can be operated in a manner such that the load carrying means or hook can be raised or lowered beyond a safe limit. This can result in equipment damage and/or present a hazard to personnel working on the equipment.
It is often not possible for the operator to see the position of the load carrying hook or, even when same is in sight, many other distractions occur so that the operator, inadvertently, exceeds the safe positions both upwardly and downardly.
Such hoists may include a cable and winch system extending over a single top wheel and terminating in load carrying means such as a block or hook. Alternatively, hoisting devices used for raising and lowering heavy loads, normally use a stationary block consisting of several sheaves and a travelling block also consisting of several sheaves to which the load carrying means such as a hook, is attached. The cable from the "fast" sheave is passed around these sheaves on the stationary and travelling block and results in a greater length of cable passing over the "fast" sheave in order to allow the travelling block to move a relatively short distance.
It is also desirable in many instances to accurately determine total distance of travel by the hoist cable both upwardly and downwardly so that the cable can be replaced when this distance is reached.
Prior art devices known to the applicants include ton-mile indicators such as that illustrated and described in U.S. Pat. No. 3,884,071. However, this is an involved system which measures a combination of the distance travelled and the weight carried and is not usable for total up and down distance travelled by the cable neither is it usable for upper and lower load carrying means limits.